In the processing of semiconductor wafers of silicon and the like in the manufacture of circuit chips, etching of oxide layers or films on the surface of the wafer is an important aspect of the processing.
Much of the wafer processing in the past has utilized a wet etching process which involves the spraying of liquid acids and other liquid chemicals and deionized water onto silicon wafers confined in wafer carriers of plastic capable of withstanding the deteriorating effects of strong chemicals such as acids.
One or more such wafer carriers is carried on a variable speed turntable or rotor in a closed bowl of an acid processor machine. Such a machine has many variable phases to its operation including varying the speed of the rotor, sequentially spraying various liquid processing chemicals, and nitrogen gas for drying the wafers, bowl and rotor between various wet processing phases. One form of acid processor is illustrated and described in U.S. Pat. No. 3,990,462. Also see U.S. Pat. Nos. 4,609,575; 4,682,615 and 4,691,722 for variations in spray nozzle arrangements and other facilities for wet etch processing. Also see U.S. Pat. No. 4,682,614 for a nearly horizontal machine.
Etching of silicon wafers has been carried out with plasma of certain gases. A number of wafers were disclosed to have been simultaneously etched in U.S. Pat. No. 3,879,597 using plasma techniques.
Some early work in batch etching of SiO.sub.2 with gaesous HF/H.sub.2 O was disclosed in an IBM Technical Disclosure Bulletin, Vol. 19, No. 7, December, 1976, K. D. Beyer and M. H. Whitehill. A number of wafers in a tray were placed above an HF-solution, then rinsed in DI-water, and finally dipped in a nitric acid solution.
Etching of oxide films on silicon wafers has been accomplished, in recent years, with the use of anhydrous hydrogen fluoride gas. See U.S. Pat. No. 4,749,440. The etchant hydrogen fluoride gas is usually diluted with dry nitrogen gas. A small amount of moisture, either as a vapor mixed with the hydrogen fluoride gas or contained in the oxide film being etched, is necessarily present to react with the oxide in the film to initiate the etching process.
Such previous gas phase etching of oxide films of silicon wafers has been done only on one wafer at a time, in a chamber designed for and carrying only one wafer. See the '440 patent mentioned above and also see application Ser. No. 020,473, filed Mar. 2, 1987 at the U.S. Patent and Trademark Office under common ownership with the present application.